<p class="title-p">
  选择资源分类:
  <label class="red required">*</label>
</p>
<div class="error-alert" *ngIf="expressionError&&!selectedFiles.length" > 
    <small class="error">请选择一个资源分类</small>
</div>
<div class="modal-tree checkbox-tree">
  <p-tree 
    [value]="data" 
    selectionMode="checkbox" 
    [(selection)]="selectedFiles" 
    [propagateSelectionDown] = "false"
    [propagateSelectionUp]="false"
    (onNodeSelect)="nodeSelect($event)" 
    (onNodeUnselect)="nodeUnselect($event)">
  </p-tree>
</div>
